1. Field of the Invention
The present invention relates to an organosilicon-treated pigment, a process for production thereof, and a cosmetic made therewith, and more particularly, to a new pigment and extender pigment which are smooth, superior in adhesion and spreadability, and completely free of residual hydrogen, a process for production of said pigment, and a cosmetic made with said pigment.
2. Description of the Prior Art
An organosilicon compound, especially methylhydrogenpolysiloxane, finds use as a surface treatment agent for pigments and extender pigments. The surface-treated pigments and pigment extenders are now in general use for lasting makeup and two-way type cosmetics because of their high water repellency.
The ordinary method for surface treatment does not permit the reactive Si-H groups of the silicone molecule to undergo complete reaction. The percent conversion is such that 30-60% of hydrogen remains unreacted. This holds true of methylhydrogenpolysiloxane. Its crosslinking reaction does not proceed completely on account of steric hindrance, with hydrogen remaining unreacted. Pigments or extender pigments with such residual hydrogen give off gaseous hydrogen (which presents a danger of explosion) upon processing into cosmetics under alkaline or acidic conditions. Moreover, the resulting cosmetics expand their containers or cloud the compact glass as time goes by.
Those pigments vulnerable to heat, such as yellow oxide, Prussian blue, and Red 202 (Lithol Rubine BCA), may be treated at a low temperature by the aid of a catalyst. A disadvantage of this method is that the catalyst remains unreacted.
There has been proposed a process for treatment with methylhydrogenpolysiloxane to improve the percent conversion by addition of an acid substance or an alkali metal hydroxide. A disadvantage of this process is that methylhydrogenpolysiloxane undergoes crosslinking polymerization which gives rise to silicone resin of reticulate three-dimensional structure. This silicone resin forms particles, which in turn bring about the strong coagulation of pigment particles. Therefore, the resulting treated pigment feels rough and is very poor in spreadability and adhesion to the skin.
Another improvement is by mechanochemical treatment that employs a jet atomizer. The percent conversion of methylhydrogenpolysiloxane by this method is still as low as 20-70%, depending on the kind of pigment for treatment. Hence, the above-mentioned problem associated with residual hydrogen remains unsolved. Moreover, the mechanochemical treament resorting to crushing deforms the particles of pigment or extender pigment. This is disadvantageous to a pigment or extender pigment composed of flaky or needlelike particles. In addition, the mechanochemical treatment requires special facilities which are not suitable for production of a variety of products in small quantities.